Biofilters are used to purificate odorous and VOC (volatile organic compound) gases and air. The technique is to run unpurified gases through the biomaterial which purifies the gases. Biofilters have been designed primarily for odour control at wastewater treatment plants, rendering plants, composting operations, chemical plants, paint industry, biogas fermentation plants, waste handling plants, livestock industry, food industry, beverage industry, etc. A common prior art technique is to build a building which has open airspace at the bottom of the building. On top of the airspace is metal grid or such, which holds the filter media/biomaterial on its place. The unpurified gases are led to the airspace and from there upwards through the filter media/biomaterial. On top of the filter media/biomaterial the purified gases are collected and led to the open air.
There are also transportable versions of the biofilters. These solutions are constructed for example in a freight container. The construction of the freight container is basically the same as described above. These structures are heavy to transport and are not collapsible.
Prior art biofilters are known for example from DE 19526788C and DE 4032234A.
In DE 19526788C is described a system and process for purifying gases. This biofilter is made of steel and has a removable lid. The unpurified gases are passed into a gas inlet space above the filter bed, sprayed with a water, led through the filter bed and directed out from the air space at the bottom of the structure.
In DE 4032234A is described a system where the gases are blowed to the airspace under the filter media. At the same time the gases are humidified. The filter media is stored in a firm/solid structure and the purified gases are released to the open air above the biofilter.
In both of these prior art solutions the filter media is stored in a hard container witch is a fixed/non detachable part of the whole structure. These prior art solutions are also expensive to manufacture and tricky to maintain.
Prior art biofilters are also made by welding hard plastic. This construction is more expensive to manufacture and they are not mechanically so well suitable for stacking the biofilters.
Solutions with solid house-like structures often include perforated pipelines under the filter media. These structures are expensive to build and have a poor maintainability. These structures require also a large area for themselves which is not cost effective. Changing the filter media in all prior art solutions is a complicated and dirty work. If the weather conditions requires covering of the biofilter with a lid or such the maintenance is even more complicated. This means interruptions in the purification processes in the installations they are used in.